/Engine/Source/Editor/EditorWidgets/Public/Filters/CustomClassFilterData.h
Or you can provide aUClass, a Category and a Color to identify the filter
FCustomClassFilterData ( [UClass](API\Runtime\CoreUObject\UObject\UClass) * InClass, [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [FFilterCategory](API\Developer\ToolWidgets\Filters\FFilterCategory) > InCategory, [FLinearColor](API\Runtime\Core\Math\FLinearColor) InColor )